1. Field of the Invention
The invention relates generally to aerial and die-mount cams and more particularly to improvements in die-mount roller cams having wear plates configured and disposed to facilitate assembly with increased precision and to provide an increased load-bearing capacity and a prolonged useful life.
2. Background Art
Since many large presses are capable of exerting force in only a vertical direction, mechanisms have been developed to make efficient use of components of the vertical force to provide useful forces in other directions. These are used to operate tools for such manufacturing operations as punching, trimming, stamping and bending.
Common among the mechanisms used are aerial and die-mount cams. Each of these typically includes three basic portions. An upper portion is connected to an upper shoe of a press, and a lower portion is connected to a lower shoe. A central portion, or slide, to which a tool can be secured, slidably resides between the upper and lower portions. If the upper portion is a cam adapter and the lower portion is a driver, the mechanism is commonly referred to as an aerial cam. If the upper portion is a driver and the lower portion is a cam adapter, the mechanism is referred to as a die-mount cam.
The slide, with its attached tool, is driven in a nonvertical direction when the upper portion is forced vertically toward the lower portion by the press. If the tool is, for example, a punch, it will be driven through a workpiece, for example, a metal panel, under urging of the press. The punch is typically withdrawn from the metal panel as the slide is retracted under a stripping force provided by a return spring. Return springs are subject to failure, however, and such failures can damage the roller cam and workpieces. At best, failed return springs need replacement, resulting in press downtime.
Wear plates are used between sliding surfaces that contact one another to reduce friction and increase element longevity. The wear plates must be capable of bearing the rated cam unit force supplied by the press and of dissipating thermal energy resulting from friction. Wear plates are typically secured in place with screws, and there is a danger that screws can become loose when brought under stress as a sliding surface is repeatedly forced against a wear plate and repeatedly forced to slide along it. Such an event could result in press downtime and damage to the roller cam and workpiece. Also, as their name implies, wear plates wear out with use and must be periodically replaced, which often requires disassembly and reassembly time.
Many aerial and die-mount cams have wear plates that are mounted so that their working surfaces are laterally horizontal. These wear plates provide support for the slide but provide little resistance to lateral yawing or vertical pitching of the slide. Any amount of pitching or yawing of the slide is likely to result in a proportional amount of inaccuracy in directing a tool to its desired target.
Commonly, present aerial and die-mount cams have profiles that are high enough to prevent their use in small presses. Many also have no provision for retracting their slides if the return springs used for this purpose jams or breaks.